The present invention relates to the automatic adjustment of the air-fuel ratio (AFR) of an electronic fuel injected vehicle/engine to a target value using a vehicle/engine load device, a fuel flow modifying apparatus and a programmed digital computer.
The function of an electronic fuel injection system is to control an engine""s air-fuel ratio to appropriate target specifications. In an engine that is operating under normal conditions, the air-fuel ratio should be controlled to remain within acceptable limits. Changing other engine operating conditions such as valve timing or the exhaust system design to enhance vehicle performance can alter the air-fuel ratio significantly. In order to optimize vehicle performance under these new engine operating conditions, the fuel flow to the engine must be modified to re-establish an appropriate target air-fuel ratio over the operating range of the vehicle.
After an engine reaches operating temperature, there are two primary variables that establish the operating condition, (1) the throttle position (as a function of percent open) and (2) the crankshaft speed in revolutions per minute (RPM).
Throttle position (expressed as a percentage of open) controls the flow of air into the engine by restricting intake air flow. At 0 percent throttle position the air flow is restricted sufficiently to keep the engine idling with no load. At 100 percent throttle position, the air flow restriction is at a minimum, thereby allowing the engine to develop maximum torque. Crankshaft speed (RPM) is directly related to the amount of air the engine pulls through the throttle body. The higher the RPM, the higher the air flow into the engine. The combination of throttle position and RPM determines the flow rate of air into the engine.
The electronic fuel injection system controls the fuel flow into the engine. The Engine Control Unit (ECU) is the part of the electronic fuel injection system that controls the fuel flow rate by applying the proper control signals to the fuel injectors. The fuel flow rate is based on a number of variables, two of which are throttle position and RPM. Typical engine control units do not allow adjustment of the internally stored fuel flow tables. However, as indicated above, adjustment of fuel flow may become necessary when performance enhancements are added to the vehicle/engine.
One type of fuel flow modifying apparatus is an injector signal modifier (ISM). Injector signal modifiers are available to modify the relationship of the engine control unit signals to the fuel injectors thus allowing the adjustment of fuel flow. When applied to a fuel-injected engine, an injector signal modifier needs to be calibrated or mapped to adjust fuel flow for a range of throttle positions and RPM. The calibration or mapping process is referred to as xe2x80x9ctuningxe2x80x9d the fuel injection system. An operator controls engine load, throttle position and RPM. The operator observes the air-fuel ratio (or some other parameter, such as oxygen (O2) in the exhaust, that is indicative of the air-fuel ratio) and adjusts the internally stored table (map) in the injector signal modifier. The procedure is repeated for all operating conditions, which results in a long and tedious fuel injector tuning operation.
In particular, the manual tuning of a fuel injection system in the prior art consists of setting the RPM of the engine to a fixed level, then advancing the throttle from one fixed position to the next. At each throttle position for the same engine RPM, the stored value in the corresponding cell of the injector signal modifier is adjusted by the operator to achieve the target air to fuel ratio.
The present invention is embodied in a method and apparatus for automatic tuning of fuel injected engines. In one embodiment of the present invention, the fuel injection system is tuned by holding the engine throttle in a first position and having a digital computer vary the engine RPM. For each value of engine RPM, the corresponding cell of the map is computed for storage in the injector signal modifier map. After all values of engine RPM had been attained, the operator is instructed by the digital computer to advance the throttle to a second position. While the throttle is in the second position the engine RPM is varied between lowest and highest values over the engine operating range. For each value of engine RPM (while at the second throttle position), the corresponding cell of the map is computed for storage in the injector signal modifier map. In such manner, for each value of throttle position and engine RPM, values for corresponding cells of the map are computed and stored in the injection signal modifier map to achieve fuel injection tuning.